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29 July 2004 Active control of a two-dimensional periodic structure
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Conventional passive periodic structures exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called the "Pass Bands" and wave propagation is completely blocked within other frequency bands called the "Stop Bands." In this paper, the emphasis is placed on actively controlling the spectral width and location of the pass and stop bands in two-dimensional periodic structures depending on the direction of wave propagation. In this paper, an idealized periodic structure is considered which consists of a two-dimensional array of masses that are coupled by sets of active and passive springs with the active springs distributed in a periodic manner. The unique filtering characteristics of the active periodic structure are demonstrated by evaluating the phase constant surfaces and directivity plots, and verified by computing the response to point harmonic loading and modal density. The presented examples demonstrate the feasibility of tuning the spectral width and location of the pass and stop bands according to the nature of the external excitation. This unique directional behavior makes the application of the two-dimensional periodic structures as directional mechanical filters potentially attractive for various applications such as panels with active periodic stiffeners for effective vibration isolation and acoustic stealth.
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Youngjoon Kim and Amr M. Baz "Active control of a two-dimensional periodic structure", Proc. SPIE 5386, Smart Structures and Materials 2004: Damping and Isolation, (29 July 2004);

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